T-Mobile today announced enhanced coverage in three major metro areas including Seattle, paving the way for the nation’s fourth-largest carrier to bring on Apple’s iPhone.

Customers in Seattle, Atlanta and Minneapolis will experience a “significant speed boost on our network” and will now be able to use their unlocked iPhones on the T-Mobile network. Bellevue-based T-Mobile expects to cover 100 million people with its new network by the end of 2012 and has improved coverage in 18 major U.S. metro areas.

The company has been recently rolling out its HSPA+ 4G network improvements to enable faster speeds for customers that already have unlocked iPhones. T-Mobile does not offer 4G LTE, but the HSPA+ is comparable in terms of speed. Today’s announcement also notes that internal tests of unlocked iPhones running on T-Mobile’s 4G network recorded on average 70 percent faster download speeds than the iPhones on AT&T’s network.

The company will debut a 4G LTE network early next year, and it wouldn’t be surprising to see it happen at the same time T-Mobile launches Apple products.

Taylor Soper is GeekWire's managing editor, responsible for coordinating the newsroom, planning coverage, and editing stories. A native of Portland, Ore., and graduate of the University of Washington, he was previously a GeekWire staff reporter, covering beats including startups and sports technology. Follow him @taylor_soper and email taylor@geekwire.com.